Annular electrode assembly for a plethysmograph



Jan. 2, 1968 EITEPAN FIGAR 3,361,129

ANNULAR ELECTRODE ASSEMBLY FOR A PLETHYSMOGRAPH Filed July 14, 1965 40 31 FIG. 4

INVENTOR. Szpan 1 23012" United States Patent 3,361,129 ANNULAR ELECTRODE ASSEMBLY FOR A v PLETHYSMOGRAPH Stpz'rn Figar, Prague, Czechoslovakia, assiguor to Ceskosloveuslra akademie ved, Prague, Czechoslovakia Filed July 14, 1965, Ser. No. 471,891 Claims priority, application Czechoslovakia, July 25, 1964, 4,305/64 9 Claims. (Cl. 128-2.05)

This invention relates to the investigation of blood circulation and of other factors which affect the volume of portions of the human body, and particularly to plethysmography.

In its more specific aspects, the invention is concerned with an adjustable annular electrode assembly for a plethysmograph in which changes in the distance between a sensing electrode and a portion of the body cause variations in the capacitance of a circuit, and which is equipped with indicating or recording means for displaying the capacitance changes as a function of the varying distance.

It is known to provide such a plethysmograph with an annular electrode into which a finger or similar body part may be inserted for measurement of the expansion and contraction of the finger with the pulsation of the blood. The sensitivity of the known devices is rather low, and they do not permit investigation of the differences in the volume changes occuring in different portions of a finger.

Among the important objects of this invention is the provision of an electrode assembly for a plethysmograph and the like which is more sensitive than the known devices and which yields useful data on localized volume changes.

It is a more specific object of the invention to provide a multiplicity of electrodes electrically insulated from each other which may be placed very closely to the finger surface and spacedly conform to the same.

With these and other objects in view, the invention, in one of its aspects, resides in an electrode assembly in which a plurality of electrode members is angularly spaced about the axis of a passage through a rigid annular support, Resilient fasteners secure the electrode members to the support in the passage. Pressure devices are interposd between the support and respective electrode members for moving the associated members in a direction toward the axis against the resilient force of the fasteners. The support, the fasteners, and/or the pressure device electrically insulate the electrode members from each other.

Other features and advantages of this invention will hereinafter become more fully apparent from the following description of the annexed drawings which illustrate preferred embodiments, and wherein:

FIG. 1 shows an annular electrode assembly of the invention in plan view;

FIG. 2 shows the device of FIG. 1 in elevation, and partly in section on its axis;

FIG. 3 illustrates a modified annular electrode assembly in fragmentary plan section on its median radial plane; and

FIG. 4 illustrates a sensing device for a plethysmograph mainly consisting of electrode assemblies of the type shown in FIGS. 1 and 2 in elevation.

Referring now to the drawing in detail, and initially to FIGS. 1 and 2, there is shown an annular element of the sensing device illustrated in FIG. 4. An outer support ring is a low, hollow metal cylinder. One of its axially terminal faces has an integral annular ridge 11, and the other terminal face has a recess 12 shaped and dimensioned to receive the ridge 11 of another identical ring 10 in c0- axial engagement.

Three identical spacers of resilient insulating material such as rubber or another elastomer are secured to 3,361,129 Patented Jan. 2, 1968 the inner face of the ring 10 by an adhesive, The spacers are segments of a ring of I-shaped cross section as best seen in FIG. 2. The width of the two flange portions of each spacer is not quite equal to the axial height of the ring 10, and the web portion extends in the median radial plane of the ring 10.

The three spacers 20 are offset from each other in a circumferential direction, and their radially inner flange portions carry circumferentially and axially coextensive electrode plates 36 which are attached to the spacers by adhesive. Each electrode plate 30 is a segment of a hollow cylinder.

Threaded radial bores in the ring 10 are aligned with openings in both flanges of the spacers 2t) and receive screws 40 of rigid insulating material such as non-plasticized polyvinyl chloride. The heads of the screws 40 are accessible outside the ring 10. The free ends of the screw shanks are normally in abutting engagement with the electrodes 30.

Three screws 40 are associated with each spacer 20 and the attached electrode plate 31). The nine screws are uniformly angularly offset about the axis of the ring 10, and are arranged in two axially spaced planes. The two circumferentially outer screws 40 associated with the same electrode plate 3h are in one of the planes, and the circumferentially central screw is in the other plane.

A lead 31 is conductively secured to each electrode plate and passes radially outwardly through the two flanges of the associated spacer, and through the ring 1t) from which each lead 31 is insulated in a conventional manner, not shown.

Any number of the assemblies shown in FIGS. 1 and 2 may be combined to form a sensing device as shown in FIG. 4. The illustrated device has six electrode assemblies, each identical with that described in more detail above, but only the six support rings 10 have been shown for the sake of clarity. The screws 4t) and leads 31 have been omitted.

The several rings 10 are coaxially juxtaposed, and their ridges 11 and recesses 12, not visible in FIG. 4, are conformingly engaged. The ends of the tubular body so formed are provided with metallic covers 18, 19 coaxially aligned with the ringsltl by ridges 11 and recesses 12. Each cover is basically a fiat circular disk formed with a central circular aperture 28, 29 whose rim is thickened. The diameter of each aperture 28, 29 is somewhat smaller than the diameter of the generally cylindrical passage defined by the electrode plates 30 in the relaxed condition of the spacers 20, and selected to hold an inserted finger or the like in a fixed position relative to the rings 10.

Each of the eighteen electrode plates 30 of the sensing device shown in FIG. 4 may be moved radially toward the surface of the inserted finger by turning the associated three screws 40 an equal number of turns. The plate may also be tilted to some extent about two axes at right angles to each other to bring it as close as possible to a surface element of the finger without touching the same.

Since the sensitivity of the device is inversely related approximately to the square of the average distance between electrode and finger surface, the improvement in sensitivity achieved by the adjustability of the multiple electrode plates is evident. The eighteen leads may be connected to a suitable capacitance bridge equipped with an eighteen-channel recorder to provide individual readings of volume changes in eighteen different areas on the inserted finger.

Obviously, useful readings can be obtained from a single electrode assembly of the type shown in FIGS. 1 and 2 when equipped with a single cover 18 or 19, or with any other means for holding an engaged finger in a stable spatial relationship to the ring 10.

The modified electrode asembly illustrated in FIG. 3

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functions in the same manner as described above, and achieves the same results. Its support ring 19 is of glass, but other insulating material may be used if so desired. Three plugs of elastomeric material are fastened to the inner cylindrical face of the ring 10 at uniform distances by screws 26.

Three electrode plates are each made of a spring metal strip whose central portion is bent into a circular arc, whereas the two ends extend radially outward, and engage respective faces of two plugs 25 under the circumferential spring tension of the electrode plate.

Three metal screws which engage non-illustrated internally threaded metal inserts in the glass ring Ill abut against each circularly arcuate electrode plate portion in circumferentially spaced points arranged on two axial levels in the manner evident from FIGS. 1 and 2. The three screws 40' have been indicated conventionally. A lead 31 connects each electrode plate 35 with the capacitance measuring circuit, not itself shown.

The metallic rings 19 of the sensing device shown in FIG. 4 provide electrical shielding for the electrode assemblies and may be grounded. The glass rings 10' cannot perform this function, but external shielding may be provided in an obvious manner.

Various other modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the appended claims, as only preferred embodiments have been disclosed.

What is claimed is:

1. In an electrode assembly for a plethysmograph and the like, in combination:

(a) a rigid annular Support having an axis and formed with an axial passage therethrough;

(b) a plurality of electrode members angularly spaced about said axis in said passage;

(0) resilient fastening means securing said electrode members to said support; and

(d) a plurality of pressure means interposed between said support and respective electrode members for moving said members in a direction toward said axis against the resilient force of said fastening means,

(1) at least one of said support, said fastening means, and said pressure means including means for electrically insulating said electrode members from each other.

2. In an assembly as set forth in claim 1, said fastening means including a plurality of fastening members of elastomeric material radially interposed between said support and respective electrode members, said fastening members being attached to said support and to the respective electrode members.

3. In an assembly as set forth in claim 1, said fastening means including a plurality of fastening members of elastomeric material circumferentially interposed between respective pairs of angularly spaced electrode members,

4 each fastening member being attached to said support in said passage and engaging the members of the associated pair of electrode members.

4. In an assembly as set forth in claim 1, said pressure means including three spaced threaded pressure members abuttingly engaging each of said electrode members, said pressure members engaging said support for threaded movement in a direction extending radially relative to the axis of said support, two of said three pressure members being spaced from the third pressure member in an axial direction, and two of said three pressure members being spaced from each other in a circumferential direction.

5. A sensing device for a plethysmograph and the like comprising, in combination:

(a) a plurality of rigid annular supports having a common axis and formed with respective axially aligned axial passages therethrough, said supports being juxtaposed;

(b) a plurality of electrode members angularly spaced about said common axis in the passage of each support;

(c) resilient fastening means securing said electrode members to the associated supports;

(d) a plurality of pressure means interposed between each support and the associated electrode members respectively for moving said members in a direction toward said axis against the resilient force of said fastening means; and

(e) insulating means associated with each support for electrically insulating said electrode members from each other.

6. A device as set forth in claim 5, wherein said supports are formed with axially engaged axial projections and recesses.

'7. A device as set forth in claim 6, wherein said projections and recesses are annular about said common axis.

8. A device as set forth in claim 7, wherein said supports jointly constitute a tubular body, the sensing device further comprising two covers on the axial end faces of said body, said covers being formed with apertures axially aligned with said passages and of smaller cross section.

9. A device as set forth in claim 8, wherein said apertures are substantially circular in said cross section.

References Cited UNITED STATES PATENTS 2,667,159 1/1954 Goldberg et al. l282.05 2,755,796 7/1956 Boucke 128-2 3,156,237 11/1964 Edmark 128-205 3,189,024 6/1965 Smith 128-2.05

RICHARD A. GAUDET, Primary Examiner.

W. E. KAMM, Examiner. 

1. IN AN ELECTRODE ASSEMBLY FOR A PLETHYSMOGRAPH AND THE LIKE, IN COMBINATION: (A) A RIGID ANNULAR SUPPORT HAVING AN AXIS AND FORMED WITH AN AXIAL PASSAGE THERETHROUGH; (B) A PLURALITY OF ELECTRODE MEMBERS ANGULARLY SPACED ABOUT SAID AXIS IN SAID PASSAGE; (C) RESILIENT FASTENING MEANS SECURING SAID ELECTRODE MEMBERS TO SAID SUPPORT; AND (D) A PLURALITY OF PRESSURE MEANS INTERPOSED BETWEEN SAID SUPPORT AND RESPECTIVE ELECTRODE MEMBERS FOR MOVING SAID MEMBERS IN A DIRECTION TOWARD SAID AXIS AGAINST THE RESILIENT FORCE OF SAID FASTENING MEANS, 